1. Field of the Invention
The present invention relates to an apparatus and a method for cleaning semiconductor devices, and more particularly, to an apparatus and a method for cleaning semiconductor devices where water droplets are completely eliminated after the wafer is cleaned in the course of the semiconductor manufacturing process.
2. Background of the Invention
In the course of the semiconductor manufacturing process, after a polysilicon film is formed and before a silicide film is formed on the polysilicon film, the wafer having the polysilicon film formed thereon is cleaned by means of a solution (DHF) containing deionized water (DI) and hydrofluoric acid (HF) mixed at a ratio of about one hundred to one, in order to strengthen the adhesion between the polysilicon film and the silicide film.
However, in the conventional semiconductor manufacturing process, water droplets are usually left on the polysilicon film after the wafer is cleaned by means of the DHF solution.
As shown in FIGS. 1A and 1B, a gate oxide film 110 and a polysilicon film 120 are formed on a silicon substrate 100 in serial order, and then the surface of the polysilicon film 120 is cleaned by the DHF solution. Thereafter, a silicide film 130 is formed on the polysilicon film 120. After the cleaning process, however, water droplets 121 may have remained on the surface of the polysilicon film 120 at the interface between the polysilicon film 120 and the silicide film 130 as shown in FIG. 1B.
Thereafter, a photoresist pattern 140 is formed on the silicide film 130 as shown in FIG. 1C, and then the silicon film 130 and the polysilicon film 120 are selectively etched by an isotropic plasma etch. In this case, the water droplet 121 functions in the same manner as an oxide film would during the etching process, thereby preventing the polysilicon film 120 under the water droplet 121 from being etched as shown in FIG. 1D.
Water droplets form because the wafer is not completely dried after the polysilicon film 120 is cleaned. Especially in case where the selectivity between the polysilicon film and the oxide film is high in order to prevent the gate oxide film 110 from being etched, the formation of water droplets 121 happens often, to the point where a bridge phenomenon occurs.
A bridging phenomenon means that since the polysilicon film 120 is prevented from being etched, or is partially etched, due to the existence of the water droplet 121, a polysilicon line and an adjacent line are joined to each other rather than being separated from each other.
In cleaning and drying the wafer, a robot picks up the wafer out of a cleaning container after the wafer is cleaned by means of the DHF solution, and then the wafer is dried. However, part of the deionized water is left on the polysilicon film 120 even after the drying process, thereby forming the water droplet which, as discussed above, has a critical effect on the proper formation of the semiconductor devices.
FIG. 2 schematically shows the construction of a conventional apparatus for cleaning semiconductor devices.
Referring to FIG. 2, a supply path 1 and a drain path 3 are connected to a cleaning container 10. A supply valve 20 is disposed in the supply path 1 and controls the supply of the cleaning solution into the cleaning container 10. A manually operated drain valve 40 is disposed in the drain path 3 and controls the drain of the cleaning solution from the cleaning container 10.
A supplemental valve 30 is disposed in a supplemental path 2 in parallel with the supply valve 20. The supplemental path 2 is connected to the supply path 1 at either side of the supply valve 20, so as to arrange a bypass for the cleaning solution supplied into the cleaning container 10. The supplemental valve 30 controls the supplying of the cleaning solution bypassing the supply valve 20 through the supplemental path 2.
However, in the conventional cleaning apparatus as described above, after the polysilicon film 120 has been cleaned in the cleaning container 10, and a robot picks out the wafer from the cleaning container 10, the cleaning solution is then drained out while the supply of the cleaning solution through the supply path 1 is cut off. Therefore, a fair amount of cleaning solution remains on the cleaning container 10 and is not completely eliminated during the succeeding drying process. A part of such remaining solution that is not dried forms the water droplets after the drying process.